Jet Set Willy Online
A multi-player online remake of Matthew Smith's Speccy classic, allowing up to 16 players to play simultaneously online. The game includes all the screens from JSW2 (with a few modifications), plus some new rooms added by the coders, although jokes about genetalia are employed to excess in the extra screens.
The game features many different modes including capture the flag, first person to collect x items wins, first person to room y wins. Sadly, no one is EVER online. I have tried at work, in the evenings, and at weekends, but I'm always the only player there. I find myself just wandering round an empty mansion in one player mode. If you want to do this, then there are many other sites that offer a much more playable one player version without constant gags about phalluses.
It's a shame this hasn't taken off because the concept is ingenious.